Only apply custom downmix to 5.1 audios (#11401)

Jellyfin.Api/Controllers/DynamicHlsController.cs

@@ -1712,12 +1712,11 @@ public class DynamicHlsController : BaseJellyfinApiController
 
         var channels = state.OutputAudioChannels;
 
+        var useDownMixAlgorithm = state.AudioStream.Channels is 6 && _encodingOptions.DownMixStereoAlgorithm != DownMixStereoAlgorithms.None;
+
         if (channels.HasValue
             && (channels.Value != 2
-                || (state.AudioStream is not null
+                || (state.AudioStream?.Channels != null && !useDownMixAlgorithm)))
-                    && state.AudioStream.Channels.HasValue
-                    && state.AudioStream.Channels.Value > 5
-                    && _encodingOptions.DownMixStereoAlgorithm == DownMixStereoAlgorithms.None)))
         {
             args += " -ac " + channels.Value;
         }

Jellyfin.Api/Helpers/StreamingHelpers.cs

@@ -166,6 +166,9 @@ public static class StreamingHelpers
         }
 
         var outputAudioCodec = streamingRequest.AudioCodec;
+        state.OutputAudioCodec = outputAudioCodec;
+        state.OutputContainer = (containerInternal ?? string.Empty).TrimStart('.');
+        state.OutputAudioChannels = encodingHelper.GetNumAudioChannelsParam(state, state.AudioStream, state.OutputAudioCodec);
         if (EncodingHelper.LosslessAudioCodecs.Contains(outputAudioCodec))
         {
             state.OutputAudioBitrate = state.AudioStream.BitRate ?? 0;
@@ -180,10 +183,6 @@ public static class StreamingHelpers
             containerInternal = ".pcm";
         }
 
-        state.OutputAudioCodec = outputAudioCodec;
-        state.OutputContainer = (containerInternal ?? string.Empty).TrimStart('.');
-        state.OutputAudioChannels = encodingHelper.GetNumAudioChannelsParam(state, state.AudioStream, state.OutputAudioCodec);
-
         if (state.VideoRequest is not null)
         {
             state.OutputVideoCodec = state.Request.VideoCodec;

MediaBrowser.Controller/MediaEncoding/EncodingHelper.cs

@@ -2627,7 +2627,7 @@ namespace MediaBrowser.Controller.MediaEncoding
                 && channels.Value == 2
                 && state.AudioStream is not null
                 && state.AudioStream.Channels.HasValue
-                && state.AudioStream.Channels.Value > 5)
+                && state.AudioStream.Channels.Value == 6)
             {
                 switch (encodingOptions.DownMixStereoAlgorithm)
                 {
@@ -2720,7 +2720,20 @@ namespace MediaBrowser.Controller.MediaEncoding
                 if (state.TranscodingType != TranscodingJobType.Progressive
                     && ((resultChannels > 2 && resultChannels < 6) || resultChannels == 7))
                 {
-                    resultChannels = 2;
+                    // We can let FFMpeg supply an extra LFE channel for 5ch and 7ch to make them 5.1 and 7.1
+                    if (resultChannels == 5)
+                    {
+                        resultChannels = 6;
+                    }
+                    else if (resultChannels == 7)
+                    {
+                        resultChannels = 8;
+                    }
+                    else
+                    {
+                        // For other weird layout, just downmix to stereo for compatibility
+                        resultChannels = 2;
+                    }
                 }
             }
 
@@ -6903,7 +6916,7 @@ namespace MediaBrowser.Controller.MediaEncoding
 
             var channels = state.OutputAudioChannels;
 
-            if (channels.HasValue && ((channels.Value != 2 && state.AudioStream.Channels <= 5) || encodingOptions.DownMixStereoAlgorithm == DownMixStereoAlgorithms.None))
+            if (channels.HasValue && ((channels.Value != 2 && state.AudioStream?.Channels != 6) || encodingOptions.DownMixStereoAlgorithm == DownMixStereoAlgorithms.None))
             {
                 args += " -ac " + channels.Value;
             }